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The colder the water, the more CO2 it absorbs, consequently, polar regions will be the first places where surface seawaters will become undersaturated with respect to aragonite, a form of carbonate ion used by marine organisms to make their shells and skeletons, and which decreases as CO2 invades the water. In the figure below, negative values (brown colours) indicate undersaturation, i.e. pure aragonite would dissolve. Figures a and b show the aragonite saturation state of surface waters when atmospheric CO2 reaches 567 ppmv (i.e. twice the pre-industrial value). Figures c and d shows the same combined with the effects of climate change, which intensify the phenomenon, especially in the Arctic where undersaturation will occur 10 to 30 years sooner than in the Antarctic. Ice melting in the Arctic will make wide areas of ocean available to take up atmospheric CO2. There will also be huge amounts of freshwater released which further increase acidification.For millions of years until the present day all surface and near subsurface waters were supersaturated with respect to aragonite. In 2008, we can already observe that near-subsurface waters in the Canada Basin have become undersaturated due to human CO2 emissions. The phenomenon continues at a rapid rate. Recent projections indicate that if CO2 emissions continue to rise as today, 10% of arctic surface waters will be undersaturated already by 2018, 50% by 2050 and 100% by the end of the century.

Arctic Ocean Southern Ocean (Antarctica)(J. Orr, 2008) Negative values (brown colours) indicate undersaturation, i.e. pure aragonite would dissolve. a-b shows the aragonite saturation state of surface waters when atmospheric CO2 reaches 567 ppmv (i.e. twice the pre-industrial value). c-d shows the same combined with the effects of climate change, which intensify the phenomenon, particularly in the Arctic where undersaturation will occur 10 to 30 years sooner and more intensely than in the Antarctic: ice melting in the Arctic will render wide areas of ocean available to take up atmospheric CO2, and release huge amounts of soft waters which also further increase acidification.

What do we want to learn & how?

How will ocean acidification affect Arctic pelagic organisms and communities?

Pelagic organisms are organisms that float around in the water column and, although some creatures are able to swim a little bit, for the most part these organisms are at the mercy of ocean currents. The sort of organisms we will be studying are microscopic plants (phytoplankton) and animals (zooplankton). There is some information on how ocean acidification might affect these organisms in the temperate regions, but this is one of the first studies to focus on Arctic organisms.

How will changes acidification affect biogeochemical cycling and release of climatically-important gases?

Phytoplankton are able to take up carbon dioxide from the water during photosynthesis, and all plankton release carbon dioxide to the water column when they respire. The amount of plankton, the types of plankton, and the growth (healthiness) of these plankton are important for influencing how much carbon dioxide is drawndown into the oceans from the atmosphere. Additionally some phytoplankton release gases, such as DMS (dimethyl sulphide) which is thought to be important for forming clouds in the atmosphere. If ocean acidification affects some of these organisms then this has consequence for the cycing of carbon and nutrients, as well as these other important gases.